Brazil is a wonderful place for the World Cup, the quadrennial soccer tournament that begins there on Thursday, but it could prove problematic for traveling fans who suffer from two of the most common phobias: arachnophobia and ophidiophobia, which is even harder to pronounce when a viper is slithering toward you.

The Brazilian wandering spider is of particular concern. Not only is this beast the size of a dinner plate—it is also the most venomous spider in the world, Guinness says. There is an antidote for wandering spider bites, so deaths are rare. Its venom can, however, cause erections in male victims, which seems an unnecessarily cruel blow to a man's dignity. Arachnophobes who suffer from medorthophobia are doomed.

The Brazilian wandering spider, of the Phoneutria genus, isn't afraid of entering human dwellings and has a reputation of being aggressive. It is basically an eight-legged Oakland Raiders fan. There are eight known species of Phoneutria, all of which can be found in Brazil and some of which will be trying to mate throughout the World Cup. During this period, males are more likely to be found in dark corners looking for a partner.

There are plenty of other spiders in Brazil, including tarantulas such as the Goliath bird-eater. The very thought is enough to scare an arachnophobe stiff, whether they encounter the venom of a wandering spider or not. Studies show that 50% of women and around 16% of men are scared of spiders, meaning there will be millions of anxious people in Brazil, even before World Cup matches go to extra time.

And then there is the snake thing. Brazil has lots of snakes. On one island off the coast of São Paulo, there is said to be a snake every square meter, though local rumor puts the figure as high as five a square meter. This island is more packed with snakes than the Spanish midfield is with talent. There you can find the highly venomous golden lancehead pit viper, whose bite could kill an FC Dallas fan in a matter of hours. The uninhabited island is called Ilha de Queimada Grande and it is illegal to visit without a permit so at least people who don't like snakes needn't worry about this place interfering with their World Cup itinerary.

But there is still enough to unnerve ophidiophobes back on the mainland, home of many venomous serpents, including coral snakes and vipers. The vast Amazon region in the north and the Pantanal wetlands in the west are two of the richest places on the planet in terms of biodiversity. In both places you can find the giant anaconda, a snake so big it could replace the bus that Jose Mourinho is so fond of parking in front of Chelsea's goal.

Still, it is unlikely visitors to Brazil will stumble upon any of these animals unless they deliberately set out to see them. But people with phobias don't deal in reality, or in rationality. They have no truck with platitudes such as, "That 50-foot snake is more scared of you than you are of it," or, "That dog-sized spider on your shower curtain won't bother you."

Brazil will be a treat for any World Cup visitor, but for people with phobias, the 20th edition of the tournament might be among the most daunting. The country certainly boasts more spiders and snakes than Europe, where half of all World Cups have been held. The most threatening animal there is probably a diseased sheep or a wild boar served as an undercooked sausage in a German restaurant.

Brazil has hosted the World Cup once before, in 1950; this will be the fifth time the tournament has been held in South America. Mexico has hosted twice and the U.S. once. These places, as well as Japan and South Korea—joint hosts in 2002—have their fair share of creepy crawlies, but nothing on the scale of what you can find in a place like the Amazon.

South Africa, the 2010 World Cup host, could challenge Brazil. Spectacularly dangerous wildlife graces that country, from lions and crocodiles to great white sharks and Bakkies Botha, the burly rugby star. It is rational to be afraid of some of these creatures.

The World Cup in Brazil poses more of a threat to people who suffer from atychiphobia, or the fear of failure. It could also affect those with xanthophobia, which is the fear of the color yellow: They won't relish seeing Brazil's national soccer shirt for the next month or so. Copacabana Beach would be a suitable refuge for people with vestiphobia: a fear of clothes. Carnival time is problematic for sufferers of omphalophobia and pteronophobia, who are scared of belly buttons and of being tickled by feathers, respectively.

And of course there is a strange group of people riddled with anxiety about penalty shootouts: the English. It is unlikely there will ever be a cure for that affliction.

Corrections & Amplifications The Brazilian wandering spider is the most venomous spider in the world, according to Guinness. An earlier version of this article called it the most poisonous. (June 10, 2014)

As a Rio citizen, my tendency is to attribute Will Davies' article on the abundance of snakes and spiders in Brazil to a general misconception northerners tend to have of my country being one huge jungle. What was my astonishment when driving past Rio's Botannical Garden on my way to work this morning to see firemen staging a complex operation to recue a huge anaconda from a tree.

Looks like they have some nice sized legs that would be tasty, heard spider legs are a bit peppery and don't have the salty taste of crab legs, but still you can add butter and add salt, more curious about the texture.

I'm Brazilian, and I can assure you that there are no dangerous snakes or spiders in large Brazilian cities like Rio, Sao Paulo or Curitiba. The Phoneutria spiders, although really common in rural areas, are nowhere to be found in urban centers. Aracnophobics, relax, you're not gonna see any spiders here.

I love spiders. I get beautiful banana spiders down here in South Carolina. They weave beautiful webs and attack the mosquito and beetles prevalent in the area. I've found a few black widows and brown recluses near my house and around windows which I have to be more careful around. But usually they are brown widows which look similar and have the similar markings such as the orange hourglass. My favorite spiders are the jumping spiders. They have cute faces and will sit on my window sill and hang out while I'm reading the WSJ online. They usually know their boundaries and will retreat back out the window, but come back to visit. By having spiders near my windows and doors, they serve as guards against other bugs that may try to venture in. I also have many lizards around my house which may not get along with the spiders, but they both are eating mosquitoes and beetles and other bugs which I don't like.

Are you serious when writing this article? Isn't there something more worthwhile to write about? Not all of Brasil is the rainforest, although one would expect spiders, snakes and other animals to live in the rainforest..Just like you would expect to find different types of animals in the dessert, or a temperate forest, of which the US has as well. I sure hope most of WSJ's readers find this a waste of reading time and don't actually take this seriously.

Good luck finding a spider or even a snake in Sao Paulo (Except for those at the Butantan Institute, which are properly caged)

If you feel going to the middle of the jungle, then yes, suit yourself, just don't forget to take Donovan with you.

This narrow vision of the Brazilian fauna shouldn't worry anyone. Now the soundness of the stadiums where the games are held is a different story. The corruption of the Brazilian government is scarier than any venomous spider or snake in the planet.

"There is an antidote for
wandering spider bites, so deaths are rare. Its venom can, however, cause
erections in male victims, which seems an unnecessarily cruel blow to a man's
dignity. Arachnophobes who suffer from medorthophobia are doomed."

Odd that the pharma industry has not made some sort of blood pressure drug from that spider. You would think it might be a natural since it is a vaso-dilator. Perhaps they have medorthophobia. After all, Viagra was a failed bp drug that when they tried to retrieve the stuff left with the folks in the trial they said: "No way!".

Well they may not have made it from the venom of the spider--but I believe Lisinopril, one of the most common blood pressure ACE inhibitors was synthesized from a natural substance in the venom of a Brazilian Pit Viper...

Odd that the pharma industry has not made some sort of blood pressure drug from that spider. You would think it might be a natural since it is a vaso-dilator. Perhaps they have medorthophobia. After all, Viagra was a failed bp drug that when they tried to retrieve the stuff left with the folks in the trial they said: "No way!".

@MAriana Dias You need to lighten up if only just a bit. This was a great article, most well written, and in the spirit of the WSJ of old. If I may paraphrase Mr Welch of Joe McCarthy fame, ... At long last, have you no sense of humor AT ALL?

@Rodolfo Alvarado You should look up where some of these stadiums and locales are located before deciding that there won't be some run-ins with the wild-life. If I remember right, one stadium can only be reached by boat, as the roads are in such disrepair.

Viagra was used in medical research as a tissue vasodilator. I used it decades ago in the heart lab, where I regularly created heart attacks. Discovering the mechanism by which it works won someone a Nobel prize. It's off-label use on the other love muscle won someone a *lot* of money.

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